Instrumentation

The external characteristic experimental data (rotational speed, torque, power, e. g. Fig. 3) were obtained for 28 different clocking positions of the two stators (relative range about 2.5 based on the vane pitch) with high-accuracy eddy-

current brake controlling system. Additional pressure and temperature kiel – head probes (Fig. 2) fixed at the inlet and outlet section of the turbine were used. In this case two stator fixed together were moved every 1/12 of the pitch performing 1000 measurements in every position, next the clocking position was changed by 1/6 of the pitch, the stators again were fixed and the operation was repeated until all indexing range was passed.

During tests presented in this paper supplementary measurements were per­formed. To find out if there is any influence of the indexing effect on leakage flow above the rotor blades, the pneumatic signals with the help of unsteady pressure transducers were received (Fig. 6b). The data from the pressure trans­ducer were simultaneously recorded by the digital multimeter (DC part of the signal) and the transient recorder (AC part of the signal) to obtain the maxi­mum resolution. The data acquisition was triggered by a photocell located at the hub of the rotor.

Unsteady pressure was sampled in a one-time window with a digital reso­lution of 256 points at a sampling frequency of 240 kHz. After one rotor rev-

olution, the next time-window was recorded, until 256 of these time-windows were stored.

The triggering and data acquisition systems for the thermoanemometric mea­surements were the same. For vane boundary layer phenomena identification glue-on hot-film probes were used. The results presented here were performed on the suction side of the vanes at the midspan of the ft>w channel. Addi­tionally, to find the correlation between hot-film signals and inside noise level another tests were performed including acoustic measurements with the help of 1/4” microphones perpendicularly connected to the vane surface tap tubing. The method was similar to the one used by [Sabah, Roger 2001]. The data from glue-on hot-film sensor and the microphone were sampled simultaneously at 50 kHz and next, recorded by a digital data acquisition system.

More details about data treatment methods can also be found in [Smolny, Blaszczak 1996, 1997].

Figure 6. Rotor geometry (a) and the position (b) of the unsteady pressure transducer (c)